240 ME. HAHSHAW THOMAS ON THE FOSSIL FLORA OF [June I9I3,. 



The specimens are rather fragmentary, hut show fronds which 

 are divided to the rachis into segments of somewhat unequal 

 breadth. Fine simple parallel veins traverse the segments, two 

 or three occurring in each millimetre. 



The specimens in the present collection tend to fall into two 

 groups : some having short truncated segments 10 to 25 mm. long,, 

 while the others have long linear segments 40 to 60 mm. in length. 

 When these specimens, however, are compared with examples from 

 other Yorkshire localities, it is seen that all variations in form 

 occur between similar limits. The smaller specimens may represent 

 young fronds, or the basal portions of larger ones. In one example 

 the latter is obviously the case. The longer segments, while having 

 in the main the same type of venation as the shorter, show a longi- 

 tudinal wrinkling of the lamina which gives the appearance of a 

 much coarser venation. The same segments also show the charac- 

 teristic expanded approximating bases, as figured by Prof. Seward x 

 for this species. 



One fragment of a frond was found in the grey shales, but the 

 cuticle appears to be very thin, and it was not possible to make 

 large preparations of it. The fragments which were obtained 

 showed, however, that the epidermal cells were of the rectangular 

 form seen in Nilssonia potymorjoha and N. brevis. 2 



Some excellent specimens, showing fronds of all sizes, have been 

 collected from Eoseberry Topping by Mr. H. T. Kennedy. The 

 smaller fronds have a breadth of about 12 mm., while the larger 

 examples must have measured more than 16 cm. across. They 

 exhibit characters similar to those of the Marske specimens, and 

 are chiefly remarkable for their size. 



Nilssonia oeientalis Heer. (PL XXIII, fig. 7 & PI. XXV, fig. 1.) 



1878. Nilssonia orientalis, Heer, 'Flor. Foss. Arct.' vol. v, No. 2, p. 18 & 



pi. iv, figs. 5-9. 

 1880. Nilssonia tenuinervis, Nathorst, ' Berattelse ' Ofvers. K. Svenska 



Vetensk.-Akad. Forhandl. No. 5, p. 35. 

 1882. Nilssonia joJmstrupi, Heer, ' Flor. Foss. Arct.' (Flora der Ataneschichten ') 



vol. vi, p. 44 & pi. vi, figs. 1-6. 

 1889. Nilssonia orientalis, Yokoyama, Journ. Coll. Sci. Tokyo, vol. iii, pi. xhv 



figs. 4-9. 

 1897. Nilssonia sp. cf . orientalis, Nathorst, ' Mesoz. Flor. Spitzbergens ' K. 



Svenska Vetensk.-Akad. Handl. vol. xxx, No. 1, pi. i, fig. 18. 

 1900. Nilssonia tenuinervis, Seward, Proc. Manchester Lit. & Phil. Soc. 



vol. xliv, No. 8, p. 4. 

 1900. Nilssonia tenuinervis, Seward, ' Jur. Flor. Yorks.' vol. i, p. 230 & fig. 41.. 

 1905. Nilssonia orientalis, Fontaine & Ward, U.S. Geol. Surv. Monogr. 



vol. xlviii, pi. xvi, figs. 3-9. 

 1909. Nilssoniopteris tenuinervis (pars), Nathorst, K. Svenska Vetensk.- 

 Akad. Handl. vol. xliii, No. 12, pi. vi, figs. 23 & 24. 

 1911. Nilssonia orientalis, Seward, Trans. Roy. Soc. Edin. vol. xlvii, pt. 4,. 



p. 695 & pi. iv, figs. 60, 63-65 ; pi. ix, figs. 34, 40, 42. 

 1911. Nilssonia orientalis, Thomas, Mem. Com. Geol. Russ. n. s. No. 71, 



pi. vii, fig. 1. 



1 Seward (00) pi. iv, fig. 1. 



2 Nathorst (09 l ) pi. vii, figs. 14-15 & pi. viii, figs. 1-18. 



